Cryogenic emissivity measurements of black coatings for ARC-ETCRYO from room temperature down to 90 K

With the advent of third-generation gravitational wave interferometers, such as the Einstein Telescope (ET), cryogenics will play a fundamental role. The technological leap required involves significantly larger mirrors, whose cooling demands both higher efficiency and low-noise techniques. A major challenge associated with cryogenic interferometers is the reduction of the duty cycle, driven by the long cooling time of the payloads. As demonstrated by KAGRA, high-emissivity coatings applied on the suspended cryogenic stages can significantly accelerate the cooling process. In this context, the ARC-ETCRYO project aims to validate pivotal technologies for use in ET, including a high-emissivity coating. To identify the optimal candidate, the emissivity of six different coatings was experimentally measured by exploiting the transient calorimetry method. The emissivity values are presented in the temperature range from room temperature down to K.